The physical limnology and sedimentology of Meziadin Lake, northern British Columbia, Canada

Meziadin Lake (34 km(2), 133 In maximum depth) is located on the east side of the Coast Mountains in northern British Columbia. Inflow from Strohn Creek is dominated by the nival flood, despite a glacier cover of 50.5 km(2) in the drainage basin. The nival flood generates turbid underflows in the lake that distribute sandy mud within 2 km of the point of inflow. During our study in 1999, turbidity currents and interflows along the thermocline continued intermittently through the summer, although the inflow of water and the suspended sediment loads decreased substantially. Sediment collected in traps throughout the lake indicate mass accumulation rates in the proximal region in excess of 200 g m(-2) d(-1) (11 mm) averaged over 69 d of observation during summer 1999, decreasing downtake to 1 g m(-2) d(-1) (0.06 mm) in the most distal region of the lake. The sediment trapped near the point of inflow has a strong mode of fine sand and is strongly negatively skewed, reflecting the competence of the turbidity currents. Texture of the sediments deposited on the lake floor decreases distally from material dominated by coarse silt and fine sand to clay sized material. Sub-bottom acoustic data document more than 180 m of accumulation in the proximal region, decreasing to <20 m distally, making the mean rates of accumulation since deglaciation (16 and 1.8 mm yr(-1), respectively) somewhat greater than those at present. This decrease is associated with changing environmental conditions and diversion of a significant portion of the drainage basin associated with the retreat of Strohn Glacier in the 20th century.